Ultrafast emission spectroscopy in the ultraviolet by time-gated upconversion

We have built a new apparatus to time resolve ultrafast fluorescence following ultraviolet excitation. A synchronously pumped dye laser produces optical pulses of 1-ps or 70-fs full-width half-maximum, depending upon dyes and optical configuration. These pulses are amplified at a 8.2-kHz repetition rate using a copper vapor laser-pumped multipass amplifier. The resulting amplified laser pulses are frequency doubled to obtain ultrafast pulses in the ultraviolet. This ultraviolet light is used to electronically excite a sample; the resulting fluorescence is time resolved using fluorescence upconversion as the optical gating technique. A minimum 300-fs full-width half-maximum instrument response function is obtained. After a brief introduction, we discuss the principles involved in this method of time resolving fluorescence. We review special considerations for femtosecond laser experimentation, and discuss the construction of our apparatus. Finally, as an example, we show how this system can be used to study fundamental physical processes in solution.